In recent years, as information technology has developed, interest has focused on the greater processing speeds of central processing units (CPU), as well as the increase in storage capacity of storage devices. Among these developments, magnetic disk storage devices are most often used as large capacity storage devices, and research is being performed into further increases in their speed and data density.
Magnetic read heads that use magnetoresistive (MR) effect elements are used for reading the information on the magnetic disks of magnetic disk storage devices. Magnetoresistive effect elements normally have a structure in which an antiferromagnetic layer, a pinned layer, a non-magnetic intermediate layer, a free layer, and a cap layer are stacked in that order. Due to the effect of the magnetic disk information magnetic field, the magnetization direction of the free layer is changed with relative to the magnetization direction of the pinned layer, whose magnetic force direction is fixed by the antiferromagnetic layer, and this changes the overall resistance of the magnetoresistive effect element. The electrical resistance across the magnetoresistive effect element is proportional to the relative directions of magnetization of the free and pinned layers. Therefore, as the relative orientation of magnetization of the free and pinned layers changes, the resulting change in electrical resistance can be detected as a magnetic signal.
The known formats of magnetoresistive effect elements include the current-in-plane (CIP) format in which current flows parallel to the film surfaces of the magnetoresistive effect element, the current perpendicular to plane (CPP) format in which the current flows perpendicular to the film surfaces, the giant magnetoresistive (GMR) format and the tunneling magnetoresistive (TMR) format. As a result of the high density recording capacity in recent years, the CPP-GMR format and the TMR format have become the main formats used.
As magnetoresistive effect elements become smaller, the magnetic stability of the sensor becomes worse. For example, the reduced area between the pinned layer and the AFM layer reduces the exchange coupling between these layer and, therefore, reduces the pinning strength of the sensor. Japanese Unexamined Patent Application Publication No. 2007-220154 discloses a step structure for the top surface of the pinned layer of a junction end portion in the height direction of a TMR element, wherein the pinned layer extends further from the air bearing surface than the free layer. This can increase the area of the pinned layer for improved pinning strength. However, such a design that incorporates an extended pinned layer presents its own challenges with regard to manufacturability and sensor performance.